Ya, bad form _may_ cause problems. But I'll claim that many more problems arise from doing nothing and getting really out of shape, rather than from doing one of the "wrong" things.
Besides, I can kick my (rather low) ceiling, and none of your experts will advise me on the correct form for this. Without their advice what am I supposed to do, just stop kicking my ceiling? Ridiculous.
I don't necessarily disagree with your overall message. But I do think you're undercounting the number of folks who get injured through ignorance. And I don't even necessarily mean traumatic injury. Even just enough injury or soreness to discourage them from trying things again can be problematic enough. Is kicking your ceiling really a good measure of some sort of fitness? Is it worth the risk of slipping and cracking your head? I don't know. Maybe. But it's far more risk of injury than walking around the block a few times and the vast majority of people really just need to start there.
No, you can easily cause injuries from bad form that you wouldn't have gotten simply by doing nothing. I know several people know who broke or damaged something in their bodies and a few who needed surgery to fix it due to bad form over time.
I again claim: many more problems arise from doing nothing and getting really out of shape, rather than from doing one of the "wrong" things. You know several people that have been injured, i don’t doubt this. But in the US, 40% of adults are obese[1]. Europe is better but still bad (~20%).
Obesity is rather unrelated to exercise, it is about diet primarily; one can do nothing wrt exercise and still be thin. Injuries in terms of suffering are far worse than being unfit (not necessarily obese but not exercising in general), the amount of pain is incomparable.
Besides, I can kick my (rather low) ceiling, and none of your experts will advise me on the correct form for this. Without their advice what am I supposed to do, just stop kicking my ceiling? Ridiculous.